Midline section of the corpus callosum is carried out in an effort to control multifocal epilepsy. Recently there has been renewed interest in this surgical approach, and, as a consequence, many more patients are becoming available for long-term neuropsychological study. In addition, it has recently been demonstrated that NMR Imaging allows for the verification of the extent of surgical section. Both of these developments allow for unique opportunities to examine several issues. Specifically, we propose to study (1) the neurobehavioral consequences of callosal section with particular emphasis on changes in perceptual, motor, memory, and language functions; 2) the specific function of callosal pathways both intentionally and inadvertently spared; 3) the relatively common failure of the disconnected right hemispheres to perform cognitive and perceptual tasks; and 4) the phonologic, semantic and syntactic capacity of patients with right hemisphere language. Taken together, these studies will provide insight into cortical and subcortical processes involved in normal human cognition.